1. Field of the Invention
The present invention relates to an ultrasonic device for measuring a flowing speed of a liquid or a material""s moving speed in a liquid by making use of the Doppler effect.
2. Description of the Prior Art
There are touch- and untouch-types of conventional devices for detecting a vibration displacement. Devices, for example, as an electric micrometer and a digital gauge for a small displacement, a rotary encoder for a rotation displacement, and a linear scale for a large displacement belong to the touch-type. These touch-type devices have some problems on measurement accuracy, response time, difficulty in use, durability and manufacturing. Devices, for example, as a laser-type sensor and an electroacoustic-type sensor belong to the untouch-type. The laser-type sensor has a defect that the longer the length of the laser beam, the lower the measurement accuracy because of flickering of the laser beam itself. In addition, the use of the laser-type sensor is impossible for the measurement in opaque media. The electroacoustic-type sensor has some problems on measurement accuracy, resistance for a change of circumstances, and so on. In addition, it is difficult to measure precisely and conveniently a flowing speed of a liquid by conventional devices.
An object of the present invention is to provide an ultrasonic Doppler flow-meter capable of measuring a flowing speed of a liquid or a material""s moving speed in a liquid with a high sensitivity.
Another object of the present invention is to provide an ultrasonic Doppler flow-meter capable of operating at a high frequency.
Another object of the present invention is to provide an ultrasonic Doppler flow-meter excellent in measurement accuracy, response time, durability, and manufacturing.
A still other object of the present invention is to provide an ultrasonic Doppler flow-meter easy in use and having a small size which is very light in weight and has a simple structure.
According to one aspect of the present invention there is provided an ultrasonic Doppler flow-meter comprising a substrate with a piezoelectricity, an input- and output interdigital transducers formed on a first end surface of the substrate, and signal analyzing unit. The finger direction of the output interdigital transducer is slanting to that of the input interdigital transducer. A second end surface of the substrate is in contact with a liquid. When an input electric signal with a carrier frequency is applied to the input interdigital transducers, a leaky elastic wave if excited in the substrate. The leaky elastic wave is radiated in the form of a longitudinal wave into the liquid, and reflected by a material in the liquid. The reflected longitudinal wave is detected at the output interdigital transducer as a delayed electric signal with a Doppler frequency. The signal analyzing unit senses a moving speed of the material in terms of a frequency difference between the carrier frequency and the Doppler frequency.
According to another aspect of the present invention there is provided a substrate made of a piezoelectric ceramic plate, of which the polarization axis is parallel to the thickness direction thereof.
According to another aspect of the present invention there is provided a substrate made of a double-layer body consisting of a piezoelectric layer part and a nonpiezoelectric layer part. Each layer part has an inner- and an outer end surfaces. The input- and output interdigital transducers are formed on one of the inner- and outer end surfaces of the piezoelectric layer part. The liquid is in contact with the outer end surface of the nonpiezoelectric layer part.
According to another aspect of the present invention there is provided a substrate made of a triple-zone body consisting of a first- and a second piezoelectric zone parts and a nonpiezoelectric zone part between the first- and second piezoelectric zone parts. Each zone part has two end surfaces. The input- and out put interdigital transducers are formed on one end surface of the first piezoelectric zone part and that of the second piezoelectric zone part, respectively. The liquid is in contact with the other end surface of each zone part.
According to another aspect of the present invention there is provided an ultrasonic Doppler flow-meter comprising a nonpiezoelectric plate, a first- and a second piezoelectric substrates, an input- and output interdigital transducers, and signal analyzing unit. One end surface of the nonpiezoelectric plate is in contact with a liquid. The first- and second piezoelectric substrates are formed on the other end surface of the nonpiezoelectric plate under an electrically separated condition. The input interdigital transducer is formed on one end surface of the first piezoelectric substrate. The output interdigital transducer is formed on one end surface of the second piezoelectric substrate, the finger direction of the output interdigital transducer being slanting to that of the input interdigital transducer.
According to another aspect of the present invention there is provided a material rotating itself. In this case, the signal analyzing unit senses a rotating speed of the material.
According to another aspect of the present invention there is provided a material moving in accordance with a flowing speed of the liquid. In this case the signal analyzing unit senses the flowing speed.
According to another aspect of the present invention there is provided an output interdigital transducer, of which the finger direction is vertical to that of an input interdigital transducer.
According to another aspect of the present invention there is provided an input- and an output interdigital transducers having an arch-shaped electrode pattern, respectively, and making a pair with a concentric center.
According to another aspect of the present invention there is provided a signal analyzing unit which comprises a signal generator generating the input electric signal, an amplifier amplifying the delayed electric signal, and a frequency counter detecting the frequency difference.
According to other aspect of the present invention there is provided a signal analyzing unit which comprises a signal generator generating the input electric signal, an amplifier amplifying the delayed electric signal, and a frequency to voltage converter converting the Doppler frequency to a voltage thereof. The frequency to voltage converter detects the frequency difference in terms of the voltage converted from the Doppler frequency.
According to a further aspect of the present invention there is provided a signal analyzing unit which comprises a signal generator generating the input electric signal, and a phase comparator comparing a phase of the input electric signal with that of the delayed electric signal. The phase comparator detects the frequency difference in terms of a phase difference between the input- and delayed electric signals.